Prior to signing the bill, O'Malley spoke before a standing-room-only crowd, saying, "For a free and diverse people, for people of many faiths, for a people committed to the principle of religious freedom, the way forward is always found through greater respect for the equal rights of all, for the human dignity of all."

"Religious freedom is the very reason for our state's founding, and at the heart of religious freedom is the freedom of individual conscience," he said. "If there is a thread that unites all of our work here together, it is the thread of human dignity, the dignity of work, the dignity of the job, the dignity of every child's home, the dignity of every individual. We are one Maryland, and all of us, at the end of the day, want the same thing for our children. We want them to live in a loving, caring, and committed home that is protected equally under the law. Let's sign the bill."

An amendment to the original bill postpones the first same sex ceremonies until January 2013. Same sex marriage supporters assume they will have another hurdle to jump as the law is expected to be petitioned to referendum in November.

Supporters at the bill signing said "this will end state-sanctioned discrimination."

"We're making history today, and we're making history for Maryland families, same sex couples raising children, their children, and couples who have lived together possibly for a long time and want to get married," said Baltimore City Delegate Maggie McIntosh, D-District 42.

After O'Malley signed the bill into law, Lt. Gov. Anthony Brown acknowledged that supporters have a lot of work to do.

"It's going to go to referendum. There's no doubt about that, but I think certainly the advocates ... the governor and I, we're going to do everything we can to make sure that marriage equality is the law in Maryland even after the November election," Brown said.

Earlier this week, the Maryland Board of Elections approved the language for a referendum question to put the issue before the voters in November. Opponents of same sex marriage vow to collect almost 56,000 signatures needed to put the measure on the ballot. They are expected to rely heavily on churchgoers who oppose same sex marriage as a matter of faith.

Organizers said they hope to collect nearly double the required number of signatures to ensure enough are validated by the Board of Elections by the June 30 deadline.